Matrix resins toughened with hybrid polyamide particles

ABSTRACT

Pre-impregnated composite material (prepreg) that can be cured/molded to form aerospace composite parts. The prepreg includes carbon reinforcing fibers and an uncured resin matrix. The resin matrix includes an epoxy component, polyethersulfone as a toughening agent, and a curing agent. The resin matrix is also composed of a thermoplastic particle component that includes hybrid polyamide particles wherein each hybrid particle contains a mixture of amorphous and semi-crystalline polyamide.

This application is a continuation-in-part of U.S. Ser. No. 16/135,177,filed on Sep. 19, 2018, now U.S. Pat. No. 10,465,042, which issued onNov. 5, 2019, which is divisional of U.S. Ser. No. 15/622,585, filed onJun. 14, 2017, now U.S. Pat. No. 10,106,661, which issued on Oct. 23,2018. U.S. Ser. No. 15/622,585 is a continuation-in-part of U.S. Ser.No. 15/439,981, filed on Feb. 23, 2017, now U.S. Pat. No. 10,000,615,which issued on Jun. 19, 2018. U.S. Ser. No. 15/622,585 is also acontinuation-in-part of U.S. Ser. No. 15/189,994, filed on Jun. 22,2016, now U.S. Pat. No. 10,208,176, which issued on Feb. 19, 2019. Thisapplication is also a continuation-in-part of U.S. Ser. No. 16/158,151,filed on Oct. 11, 2018, now U.S. Pat. No. 10,577,472, which issued onMar. 3, 2020, which is a continuation-in-part of U.S. Ser. No.15/886,008, filed on Feb. 1, 2018.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates generally to pre-impregnated compositematerial (prepreg) that is used in making high performance compositeparts that are especially well-suited for use as aerospace components.The present invention is directed to epoxy resins that are toughenedwith thermoplastic materials and used as the resin matrix in suchprepreg. More particularly, the present invention is directed to prepregthat includes polyamide particles as one of the thermoplastic materialsused to toughen the resin matrix.

2. Description of Related Art

Composite materials are typically composed of a resin matrix andreinforcing fibers as the two primary constituents. Composite materialsare often required to perform in demanding environments, such as in thefield of aerospace where the physical limits and characteristics of thecomposite part is of critical importance.

Pre-impregnated composite material (prepreg) is used widely in themanufacture of composite parts. Prepreg is a combination that typicallyincludes uncured resin and fiber reinforcement, which is in a form thatis ready for molding and curing into the final composite part. Bypre-impregnating the fiber reinforcement with resin, the manufacturercan carefully control the amount and location of resin that isimpregnated into the fiber network and ensure that the resin isdistributed in the network as desired. It is well known that therelative amount of fibers and resin in a composite part and thedistribution of resin within the fiber network affect the structuralproperties of the part.

Prepreg is a preferred material for use in manufacturing load-bearing orprimary structural parts and particularly aerospace primary structuralparts, such as wings, fuselages, bulkheads and control surfaces. It isimportant that these parts have sufficient strength, damage toleranceand other requirements that are routinely established for such parts andstructures.

The fiber reinforcements that are commonly used in aerospace prepreg aremultidirectional woven fabrics or unidirectional tape that containsfibers extending parallel to each other. The fibers are typically in theform of a bundle of numerous individual fibers or filaments that isreferred to as a “tow”. The fibers or tows can also be chopped andrandomly oriented in the resin to form a non-woven mat. These variousfiber reinforcement configurations are combined with a carefullycontrolled amount of uncured resin. The resulting prepreg is typicallyplaced between protective layers and rolled up for storage or transportto the manufacturing facility. Combinations of carbon fibers and anepoxy resin matrix have become a popular combination for aerospaceprepreg.

Prepreg may also be in the form of short segments of choppedunidirectional tape that are randomly oriented to form a non-woven matof chopped unidirectional tape. This type of prepreg is referred to as a“quasi-isotropic chopped” prepreg. Quasi-isotropic chopped prepreg issimilar to the more traditional non-woven fiber mat prepreg, except thatshort lengths of chopped unidirectional tape (chips) are randomlyoriented in the mat rather than chopped fibers. This material iscommonly used as a sheet molding compound to form parts and molds foruse in making parts.

The compressive and tensile strengths of a cured composite part arelargely dictated by the individual properties of the reinforcing fiberand matrix resin, as well as the interaction between these twocomponents. In addition, the fiber-resin volume ratio is an importantfactor. In many aerospace applications, it is desirable that thecomposite part exhibit high compression and tensile strengths. The openhole compression (OHC) test is a standard measure of the compressionstrength of a composite material. The open hole tension (OHT) test isalso a standard measure of the tensile strength of a composite material.

In many aerospace applications, it is desirable that the composite partexhibit high compression and/or tensile strength under both roomtemperature/dry conditions and hot/wet conditions. However, attempts tokeep compression and tensile strengths high often results in negativeeffects on other desirable properties, such as damage tolerance andinterlaminar fracture toughness.

Selecting higher modulus resins can be an effective way to increase thecompression strength of a composite. However, this can result in atendency to reduce damage tolerance, which is typically measured by adecrease in compressive properties, such as compression after impact(CAI) strength. Accordingly, it is can be difficult to achieve asimultaneous increase in both the compression and/or tensile strengthswithout deleteriously affecting the damage tolerance.

Multiple layers of prepreg are commonly used to form composite partsthat have a laminated structure. Delamination of such composite parts isan important failure mode. Delamination occurs when two layers debondfrom each other. Important design limiting factors include both theenergy needed to initiate a delamination and the energy needed topropagate it. The initiation and growth of a delamination is oftendetermined by examining Mode I and Mode II fracture toughness. Fracturetoughness is usually measured using composite materials that have aunidirectional fiber orientation. The interlaminar fracture toughness ofa composite material is quantified using the G1c (Double CantileverBeam) and G2c (End Notch Flex) tests. In Mode I, the pre-crackedlaminate failure is governed by peel forces and in Mode II the crack ispropagated by shear forces.

One approach to increasing interlaminar fracture toughness for partsmade from carbon fiber/epoxy resin prepreg has been to introducethermoplastic sheets as interleaves between layers of prepreg. However,this approach tends to yield stiff, tack-free materials that aredifficult to use. Another approach has been to add thermoplasticparticles to the epoxy resin so that a resin interlayer containing thethermoplastic particles is formed between the fiber layers of the finalpart. Polyamides have been used as such thermoplastic particles. It alsohas been known to include a thermoplastic toughening agent in the epoxyresin. The toughening agent, such as polyether sulfone (PES) orpolyetherimide (PEI), is dissolved in the epoxy resin before it isapplied to the carbon fibers. Thermoplastic toughened epoxy resins,which include a combination of both thermoplastic toughening particlesand a thermoplastic toughening agent, have been used in combination withcarbon fiber to make aerospace prepreg.

The epoxy resin matrix may include one or more types of epoxy resin. Itis known that various combinations of different types of epoxy resinsmay result in a wide variation in the properties of the final compositepart. The curing agent used to cure the epoxy resin matrix can alsosubstantially affect the properties of the final composite part. Whenformulating an epoxy resin for use as the resin matrix in aerospaceprepreg, it is difficult to predict if a new combination of epoxy resintypes and curatives will provide the desired combination of propertiesrequired for aerospace parts. This is especially the case when athermoplastic toughening agent and thermoplastic particles form part ofthe epoxy resin formulation. Accordingly, there is a great deal oftesting involved when one attempts to formulate new thermoplastictoughened epoxy resins in order to determine if the resin is suitablefor use as resin matrix in aerospace prepreg.

Although existing aerospace prepregs are well suited for their intendeduse in providing composite parts that are strong and damage tolerant,there still is a continuing need to provide aerospace prepreg that maybe used to make composite parts that exhibit desirable combinations ofhigh tensile and compressive strengths (OHC and OHT) while maintaininghigh levels of damage tolerance (CAI) and interlaminar fracturetoughness (G1c and G2c).

SUMMARY OF THE INVENTION

In accordance with the present invention, pre-impregnated compositematerial (prepreg) is provided that can be molded to form compositeparts that have high levels of strength and also have high levels ofdamage tolerance and interlaminar fracture toughness.

The pre-impregnated composite materials of the present invention arecomposed of reinforcing fibers and an uncured resin matrix. The uncuredresin matrix includes a resin component made up of one or more epoxyresins, a thermoplastic toughening agent and a curing agent. The uncuredresin matrix further includes a thermoplastic particle component whichincludes polyamide particles. In preferred embodiments, the polyamideparticles are hybrid polyamide particles that are each composed of amixture of semi-crystalline and crystalline polyamide.

The present invention also covers methods for making the prepreg andmethods for molding the prepreg into a wide variety of composite parts.The invention also covers the composite parts that are made using theimproved prepreg.

It has been found that resins having the matrix resin formulation, asset forth above, can be used to form prepreg that can be molded to formcomposite parts that have unexpectedly high levels of interlaminarfracture toughness.

The above described and many other features and attendant advantages ofthe present invention will become better understood by reference to thefollowing detailed description when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an aircraft, which depicts exemplaryprimary aircraft structures that can be made using composite materialsin accordance with the present invention.

FIG. 2 is a partial view of a helicopter rotor blade, which depictsexemplary primary aircraft structures that can be made using compositematerials in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Uncured epoxy resin compositions in accordance with the presentinvention may be used in a wide variety of situations where athermoplastic-toughened epoxy resin matrix is desired. Although theuncured epoxy resin composition may be used alone, the compositions aregenerally used as a matrix resin that is combined with a fibrous supportto form composite material composed of the fibrous support and the resinmatrix. The composite materials may be in the form of a prepreg,partially cured prepreg or a completely cured final part. The term“uncured”, when used herein in connection with: prepreg; the resinbefore impregnation into the fibrous support; the resin matrix that isformed when the fibrous support is impregnated with the resin; orcomposite material, is intended to cover items that may have beensubjected to some curing, but which have not been completely cured toform the final composite part or structure.

Although the uncured composite materials may be used for any intendedpurpose, they are preferably used in making parts for aerospacevehicles, such as commercial and military aircraft. For example, theuncured composite materials may be used to make non-primary (secondary)aircraft structures. However the preferred use of the uncured compositematerial is for structural applications, such as primary aircraftstructures. Primary aircraft structures or parts are those elements ofeither fixed-wing or rotary wing aircraft that undergo significantstress during flight and which are essential for the aircraft tomaintain controlled flight. The uncured composite materials may also beused for other structural applications to make load-bearing parts andstructures in general.

FIG. 1 depicts a fixed-wing aircraft at 10 that includes a number ofexemplary primary aircraft structures and parts that may be made usinguncured composite materials in accordance with the present invention.The exemplary primary parts or structures include the wing 12, fuselage14 and tail assembly 16. The wing 12 includes a number of exemplaryprimary aircraft parts, such as ailerons 18, leading edge 20, wing slats22, spoilers 24 trailing edge 26 and trailing edge flaps 28. The tailassembly 16 also includes a number of exemplary primary parts, such asrudder 30, fin 32, horizontal stabilizer 34, elevators 36 and tail 38.FIG. 2 depicts the outer end portions of a helicopter rotor blade 40which includes a spar 42 and outer surface 44 as primary aircraftstructures. Other exemplary primary aircraft structures include wingspars, and a variety of flanges, clips and connectors that connectprimary parts together to form primary structures.

The pre-impregnated composite materials (prepreg) of the presentinvention may be used as a replacement for existing prepreg that isbeing used to form composite parts in the aerospace industry and in anyother application where high structural strength and damage tolerance isrequired. The invention involves substituting the resin formulations ofthe present invention in place of existing resins that are being used tomake prepreg. Accordingly, the resin formulations of the presentinvention are suitable for use as the matrix resin in conventionalprepreg manufacturing and curing processes.

The pre-impregnated composite materials of the present invention arecomposed of reinforcing fibers and an uncured resin matrix. Thereinforcing fibers can be any of the conventional fiber configurationsthat are used in the prepreg and composite sheet molding industry.Carbon fibers are preferred as the reinforcing fibers.

A preferred resin used to form the resin matrix (matrix resin) includesa resin component that is made up of a hydrocarbon epoxy novolac resinin combination with a trifunctional epoxy resin and optionally atetrafunctional epoxy resin. The matrix resin further includes a hybridthermoplastic particle component, a thermoplastic toughening agent and acuring agent.

The hydrocarbon epoxy novolac resin preferably has a dicyclopentadienebackbone and is available commercially from Huntsman Corporation (TheWoodlands, Tex.) as TACTIX 556. This type of hydrocarbon novolac resinis referred to herein as a dicyclopentadiene novolac epoxy resin. Thechemical formula for TACTIX 556 is

TACTIX 556 is an amber to dark colored semi-solid hydrocarbon epoxynovolac resin that has an epoxy index (ISO 3001) of 4.25 to 4.65 eq/kgand epoxy equivalent (ISO 3001) of 215-235 g/eq. The viscosity of TACTIX556 at 79° C. (ISO 9371B) is 2250 mPa s. Dicyclopentadiene epoxy novolacresins other than TACTIX 556 may be used in place of TACTIX 556 providedthey have the same chemical formula and properties. For example, anothersuitable dicyclopentadiene epoxy novolac resin is XD-1000-2L which isavailable commercially from Nippon Kayaku Co., Ltd (Chiyoda-ku, Tokyo).TACTIX 556 is the preferred hydrocarbon epoxy novolac resin for use inaccordance with the present invention.

When a tetrafunctional epoxy resin is included in the preferred resincomponent, the amount of hydrocarbon epoxy novolac resin present in theuncured resin may vary from 8 to 20 weight percent based on the totalweight of the uncured resin matrix. Preferably, the uncured resin willcontain from 10 to 17 weight percent dicyclopentadiene hydrocarbon epoxynovolac resin. Uncured resin formulations that contains from 13 to 15weight percent dicyclopentadiene hydrocarbon epoxy novolac resin areparticularly preferred. In this embodiment of the invention, which isreferred to herein as the DEN/TRIF/TETF matrix resin, the uncured resincomponent is composed of dicyclopentadiene epoxy novolac resin, atrifunctional epoxy resin and a tetrafunctional epoxy resin.

In the DEN/TRIF/TETF matrix resin, a preferred exemplary trifunctionalepoxy resin is triglycidyl para-aminophenol. Triglycidylpara-aminophenol is available commercially from Huntsman AdvancedMaterials (The Woodlands, Tex.) under the trade name Araldite MY0510.Another suitable trifunctional epoxy resin is triglycidylmeta-aminophenol. Triglycidyl meta-aminophenol is available commerciallyfrom Huntsman Advanced Materials (The Woodlands, Tex.) under the tradename Araldite MY0600 and from Sumitomo Chemical Co. (Osaka, Japan) underthe trade name ELM-120. Other trifunctional epoxy resins may be usedprovided that they have properties that are the same or similar to theproperties of triglycidyl para-aminophenol or triglycidylmeta-aminophenol.

In the DEN/TRIF/TETF matrix resin embodiment, an exemplarytetrafunctional epoxy resin isN,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane (TGDDM) which isavailable commercially as Araldite MY720 and MY721 from HuntsmanAdvanced Materials (The Woodlands, Tex.), or ELM 434 from SumitomoChemical Industries, Ltd. (Chuo, Tokyo). Other tetrafunctional epoxyresins may be used provided that they have properties that are the sameor similar to the properties ofN,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl methane.

In the DEN/TRIF/TETF matrix resin, the total amount of trifunctional andtetrafunctional epoxy resin may vary from 35 to 45 weight percent basedon the total weight of the uncured resin. It is preferred that that theweight ratio between the trifunctional and tetrafunctional resins befrom 1.0:1.5 to 1.5:1.0. It is particularly preferred that the weightratio between the trifunctional and tetrafunctional resins be from1.1:1.0 to 1.3:1.0.

In another preferred embodiment of the invention, the resin componentcontains only dicyclopentadiene novolac epoxy resin and triglycidylaminophenol epoxy resin. In the resin component of this embodiment,which is referred to herein as the DEN/TRIF matrix resin, thedicyclopentadiene novolac epoxy resin is present in the range 4 wt % to30 wt %, based on the total weight of the uncured resin matrix.Preferably, the dicyclopentadiene novolac epoxy resin is present in therange 17 wt % to 27 wt %, based on the total weight of the uncured resinmatrix. More preferably, the dicyclopentadiene novolac epoxy resin ispresent in the range 20 wt % to 24 wt %, based on the total weight ofthe uncured resin matrix.

In the DEN/TRIF matrix resin, the triglycidyl aminophenol epoxy resin ispresent in the range 20 wt % to 55 wt %, based on the total weight ofthe uncured resin matrix. Preferably, the triglycidyl aminophenol epoxyresin is present in the range 26 wt % to 36 wt %, based on the totalweight of the uncured resin matrix. More preferably, the triglycidylaminophenol epoxy resin is present in the range 29 wt % to 33 wt %,based on the total weight of the uncured resin matrix. Triglycidylmeta-aminophenol is the preferred type of triglycidyl aminophenol epoxyresin for the DEN/TRIF matrix resin.

In the DEN/TRIF matrix resin, the weight ratio of triglycidylaminophenol epoxy resin to dicyclopentadiene novolac epoxy resin mayvary from 1:1 to 10.5:1. The preferred weight ratio range of triglycidylaminophenol epoxy resin to dicyclopentadiene novolac epoxy resin is from1.2:1 to 2.5:1. Most preferred is a weight ratio of triglycidylaminophenol epoxy resin to dicyclopentadiene novolac epoxy resin that isabout 2.0:1.

The uncured resin matrix in accordance with the present invention alsoincludes a thermoplastic particle component that contains one or moretypes of thermoplastic particles. Exemplary thermoplastic particles arepolyamide particles which are formed from the polymeric condensationproduct of bis(4-aminocyclohexyl)methane, including methyl derivativesand an aliphatic dicarboxylic acid selected from the group consisting ofdecane dicarboxylic acid and dodecane dicarboxylic acid.Bis(4-aminocyclohexyl)methane, and methyl derivatives thereof, arereferred to herein as the “amine component”.Bis(4-aminocyclohexyl)methane is also known as4,4′-diaminocyclohexylmethane. This type of polyamide particle and themethods for making them are described in detail in U.S. Pat. Nos.3,936,426 and 5,696,202, the contents of which are hereby incorporatedby reference.

The formula for the amine component of the polymeric condensationproduct is

where R₂ is hydrogen and R₁ is either methyl or hydrogen.

When R₁ is methyl and R₂ is hydrogen in formula AC-G, the formula forthe resulting monomeric unit of the polymeric condensation product maybe represented as follows:

The molecular number of the polymeric condensation product will rangefrom 14,000 to 20,000 with a molecular numbers of about 17,000 beingpreferred.

The polyamide particles should have particle sizes of below 100 microns.It is preferred that the particles range in size from 5 to 60 micronsand more preferably from 10 to 30 microns. It is preferred that theaverage particle size is from 15 to 25 microns. The polyamide particlesmay be regular or irregular in shape. For example, the particles may besubstantially spherical or they can be particles with a jagged shape.

One exemplary polyamide particle is made from polyamide where the aminecomponent of the polymeric condensation product has the above formula(AC-G) in which R₁ both are methyl and R₂ both are hydrogen. Suchpolyamide particles may be made from the polymeric condensation productof 3,3′-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid. The polyamide particles are made by combining, in aheated receiving vessel, 13,800 grams of 1,10-decane dicarboxylic acidand 12,870 grams of 3,3′-dimethyl-bis(4-aminocyclohexyl)methane with 30grams of 50% aqueous phosphoric acid, 150 grams benzoic acid and 101grams of water. The mixture is stirred in a pressure autoclave untilhomogeneous. After a compression, decompression and degassing phase, thepolyamide condensation product is pressed out as a strand, passed undercold water and granulated to form the polyamide particles. Polyamideparticles where R₁ both are methyl and R₂ both are hydrogen can also bemade from GRILAMID TR90, which is commercially available from EMS-Chime(Sumter, S.C.). GRILAMID TR90 is the polymeric condensation product of3,3′-dimethyl-bis(4-aminocyclohexyl)-methane and 1,10-decanedicarboxylic acid.

Another exemplary polyamide particle is made from polyamide where theamine component of the polymeric condensation product has the aboveformula (AC-G) in which R₁ and R₂ are both hydrogen. Such polyamideparticles may be made in the same manner as described above, except thatpolyamide is the polymeric condensation product ofbis(4-aminocyclohexyl)-methane and 1,10-decane dicarboxylic acid. Theformula for the amine component of this preferred polymeric condensationproduct is

Formula AC-I corresponds to the preceding general formula (AC-G) whereR₁ and R₂ are hydrogen. In addition, the hydrogen groups that arepresent at the 2, 5 and 6 positions on the cyclohexane groups, which areimplied in the general formula (AC-G), are specifically shown in formulaAC-I.

When the amine component is bis(4-aminocyclohexyl)methane (formulaAC-I), the formula for the monomeric unit of the polymeric condensationproduct of AC-I and 1,10-decane dicarboxylic acid is the same a formulaI above, except that the methyl group attached at the 3 or meta positionon each cyclohexyl groups or rings is replaced with hydrogen as shown informula II.

The molecular number of the polymeric condensation product formed frommonomeric unit II will range from 14,000 to 20,000 with a molecularnumbers of about 17,000 being preferred. The polyamide particles formedfrom this polymeric condensation product should also have particle sizesof below 100 microns. It is also preferred that the particles range insize from 3 to 60 microns and more preferably from 10 to 30 microns. Itis also preferred that the average particle size is from 15 to 25microns. The polyamide particles may also be regular or irregular inshape. For example, the particles may be substantially spherical or theycan be particles with a jagged shape.

The monomeric unit corresponding to formula II maybe in the form ofstereo isomers where the nitrogen groups attached to the cyclohexyl ringare in a cis-cis orientation, cis-trans orientation or trans-transorientation. The polyamide formed from monomer II may include one, twoor all three stereo isomers. Polyamides which contains mixtures of allthree monomeric stereo isomers tend to be amorphous, while polyamidesthat are composed predominately of one stereo isomer tend to besemi-crystalline. Processing conditions are controlled to provide thedesired mixture of stereo isomers. Trogamid® CX9704 is an exemplaryamorphous polyamide that is a mixture of all three isomeric forms offormula II. Trogamid® CX9704 is available from Evonik (Mobile, Ala.).Trogamid® CX9705 is an exemplary semi-crystalline polyamide that iscomposed predominately of the trans-trans isomeric form of formula II.Trogamid® CX9705 is available from Evonik (Mobile, Ala.).

Preferred polyamide particles are hybrid polyamide particles where eachhybrid polyamide particle contains a mixture of the above amorphous andsemi-crystalline polyamides. The hybrid polyamide particles are made bydissolving the desired amounts of amorphous and semi-crystallinepolyamide in a suitable solvent, such as ethylene glycol, to form ahybrid mixture. The hybrid mixture is then extruded and/or processedaccording to conventional polyamide processing procedures to remove thesolvent and form the desired hybrid particles that each contain amixture of amorphous and semi-crystalline polyamide.

The hybrid polyamide particles should have particle sizes of below 100microns. It is preferred that the hybrid polyamide particles range insize from 3 to 60 microns and more preferably from 10 to 30 microns. Itis preferred that the average hybrid polyamide particle size is from 15to 25 microns. The hybrid polyamide particles may also be regular orirregular in shape. For example, the hybrid polyamide particles may besubstantially spherical or they can be particles with a jagged shape.

The hybrid polyamide particles are made from a hybrid mixture thatcontains amounts of amorphous and semi-crystalline polyamide such thatthe resulting hybrid polyamide particles each contain from 20 to 80weight percent amorphous polyamide, based on the total weight of thehybrid polyamide particle, and from 20 to 80 weight percentsemi-crystalline polyamide, based on the total weight of the hybridpolyamide particle. Preferably, each hybrid polyamide particle willcontain from 65 to 75 weight percent amorphous polyamide and from 25 to35 weight percent semi-crystalline polyamide, based on the total weightof the hybrid polyamide particle. Most preferred are hybrid polyamideparticles that each contain 70±1 weight percent amorphous polyamide and30±1 weight percent semi-crystalline polyamide, based on the totalweight of the hybrid polyamide particle.

In this specification, the hybrid polyamide particles are identified bythe relative amounts of amorphous and semi-crystalline polyamide thatare present in each hybrid polyamide particle. For example, hybridpolyamide particles that contain a mixture of 70 wt % CX9704 polyamide(amorphous) and 30 wt % CX9705 polyamide (semi-crystalline) areidentified as hybrid polyamide particles 70A/30SC and hybrid polyamideparticles that contain a mixture of 30 wt % CX9704 polyamide (amorphous)and 70 wt % CX9705 (semi-crystalline) polyamide are identified as hybridpolyamide particles 30A/70SC.

Differential scanning calorimetry (DSC) is a standard test that is usedto measure the crystalline and amorphous nature of polymers. Table Asets forth the DSC test results for an exemplary amorphous polyamide(Trogamid® CX9704), an exemplary semi-crystalline polyamide (Trogamid®CX9705) and exemplary hybrid polyamides, which are composed of mixturesof Trogamid® CX9704 and Trogamid® CX9705, and which were used to makehybrid polyamide particles 70A/30SC and 30A/70SC.

TABLE A Peak 1 (Exotherm) Peak 2 (Endotherm) Temp (° C.) ΔH Temp (° C.)ΔH T_(g) (° C.) CX9705 168 15.7 247 22.2 132 CX9704 No 131 peak 70 wt %CX9704/ none 0 124 30 wt % CX9705 (70A/30SC) 30 wt % CX9704/ 180 14 12470 wt % CX9705 (30A/70SC)

The preceding description regarding the polyamide component includingpolyamide particles that are hybrid polyamide particles is not limitedto polyamides having the monomeric unit of formula II. Any polyamidethat is used in toughening epoxy resins and which can be made inamorphous and semi-crystalline forms may be used to form hybridpolyamide particles.

The thermoplastic particle component may also include one or more othertypes of polyamide particles that are typically used in thermoplastictoughened epoxy resins including, for example, polyamide (PA) 11, PA6,PA12, PA6/PA12 copolymer, PA4, PA8, PA6.6, PA4.6, PA10.10, PA6.10 andPA10.12.

An exemplary thermoplastic particle component contains a first group ofpolyamide particles which do not contain crosslinked polyamide and asecond group of polyamide particles that do contain crosslinkedpolyamide.

The first group of polyamide particles may be hybrid polyamideparticles, as described above, or any of the polyamide particle that donot contain crosslinked polyamide and which are typically used inthermoplastic toughened epoxy-based prepreg. Such particles may becomposed of polyamide (PA) 11, PA6, PA12, PA6/PA12 copolymer, PA4, PA8,PA6.6, PA4.6, PA10.10, PA6.10 and PA10.12. Non-crosslinked polyamideparticles are available commercially from a number of sources. Suitablenon-crosslinked polyamide 12 particles are available from Kobo Productsunder the trade name SP10L. SP10L particles contain over 98 wt % PA 12.The particle size distribution is from 7 microns to 13 microns with theaverage particle size being 10 microns. The density of the particles is1 g/cm³. It is preferred that the PA12 particles are at least 95 wt %PA12, excluding moisture content. It is also preferred that the hybridpolyamide particles are at least 95 wt % amorphous and semi-crystallinepolyamide, excluding moisture content.

Other suitable non-crosslinked particles are available from Arkema(Colombes, France) under the tradenames Orgasol 1002 powder and Orgasol3803 powder. Orgasol 1002 powder is composed of 100% PA6 particleshaving an average particle size of 20 microns. Orgasol 3803 is composedof particles that are a copolymer of 80% PA12 and 20% PA6 with the meanparticle size being from 17 to 24 microns. Orgasol 2002 is a powdercomposed of non-crosslinked PA12 particles that may also be used in thefirst group of particles.

A preferred non-crosslinked polyamide particles for the first group ofthermoplastic particles are polyamide 11 particles, which are alsoavailable commercially from a number of sources. The polyamide 11particles are available from Arkema (Colombes, France) under the tradename Rislan PA11. These particles contain over 98 wt % PA 11 and have aparticle size distribution of 15 microns to 25 microns. The averageparticle size is 20 microns. The density of the Rislan PAl 1 particlesis 1 g/cm³. It is preferred that the PA 11 particles are at least 95 wt% PA11, excluding moisture content.

The second group of thermoplastic polyamide particles are particles thatcontain crosslinked polyamide on the surface of the particle, in theinterior of the particle or both. The crosslinked polyamide particlesmay be made from polyamide that has been crosslinked prior to particleformation or non-crosslinked polyamide particles may be treated withsuitable crosslinking agents to produce crosslinked polyamide particles.

Suitable crosslinked particles contain crosslinked PA11, PA6, PA12,PA6/PA12 copolymer, PA4, PA8, PA6.6, PA4.6, PA10.10, PA6.10 and PA10.12.Any of the crosslinking agents commonly used to cross link polyamide aresuitable. Exemplary crosslinking agents are epoxy-based crosslinkingagents, isocyanate-based crosslinking agents, carbodiimide-basedcrosslinking agents, acyllactam-based crosslinking agents andoxazoline-based crosslinking agent. Preferred crosslinked particles arePA12 particles that contain PA12 that has been crosslinked with an epoxycrosslinking agent. The procedures used to cross link thermoplasticpolymers, including polyamide, are known. For examples, see U.S. Pat.Nos. 6,399,714, 8,846,818 and U.S. Published Patent Application US2016/0152782 A1. The contents of these three references are herebyincorporated by reference.

Crosslinked PA12 particles are available commercially from Arkema(Colombes, France) under the tradename ORGASOL 2009 polyamide powder,which is also known as CG352. The PA12 particles present in ORGASOL 2009polyamide powder are composed of at least 40% PA12 that has been crosslinked with an epoxy-based crosslinking agent. The ORGASOL 2009crosslinked polyamide particles have an average particle size of 14.2microns with only 0.2% of the particles having a diameter of greaterthan 30 microns. The melting point of ORGASOL 2009 crosslinked particlesis 180° C. The specific surface area of the ORGASOL 2009 particles is1.9 and the moisture content of the particles is 0.34%.

The crosslinked polyamide particles should each contain from 40 to 70%crosslinked polyamide. Preferably, the crosslinked polyamide particlesshould each contain from 40 to 60% crosslinked polyamide.

Preferably, both the non-crosslinked and crosslinked polyamide particlesshould have particle sizes of below 100 microns. It is preferred thatthe particles range in size from 5 to 60 microns and more preferablyfrom 5 to 30 microns. It is preferred that the average particle size isfrom 5 to 20 microns. The particles may be regular or irregular inshape. For example, the particles may be substantially spherical or theycan be particles with a jagged shape. It is preferred that thenon-crosslinked particles have an average particle size that is largerthan the crosslinked particles. Preferably, the average non-crosslinkedparticles size will range from 15 to 25 microns and the averagecrosslinked particle size will range from 10 to 20 microns.

The thermoplastic particle component is present in the range 5 wt % to20 wt %, based on the total weight of the uncured resin matrix.Preferably, there will be from 7 to 17 wt % thermoplastic particlecomponent. The relative amounts of non-crosslinked and crosslinkedparticles may be varied when a combination of crosslinked andnon-crosslinked particles are used. Weight ratios of non-crosslinkedparticles to crosslinked particles may range from 4:1 to 1.5:1.Preferably, the weight ratios of non-crosslinked particles tocrosslinked particles will range from 3.5:1 to 2.5:1. A combination ofhybrid polyamide particles and crosslinked particles is a preferredthermoplastic particle component for use with the DEN/TRIF matrix resinembodiment.

Hybrid polyamide particles are a preferred particle for use in thethermoplastic component. Hybrid polyamide particles may be used incombination with a wide variety of epoxy resin components other than theDEN/TRIF and DEN/TRIF/TETF epoxy resin components. For example, hybridpolyamide particles may be used to toughen epoxy resins that include adifunctional epoxy resin as all or part of the epoxy resin component.Difunctional epoxy resins include any suitable epoxy resin having twoepoxy functional groups. The difunctional epoxy resin may be saturated,unsaturated, cycloaliphatic, alicyclic or heterocyclic. The difunctionalepoxy may be used alone or in combination with multifunctional epoxyresins to form the resin component. Resin components that contain onlymultifunctional epoxy are also possible.

Difunctional epoxy resins, by way of example, include those based on:diglycidyl ether of Bisphenol F, Bisphenol A (optionally brominated),glycidyl ethers of phenol-aldelyde adducts, glycidyl ethers of aliphaticdiols, diglycidyl ether, diethylene glycol diglycidyl ether, Epikote,Epon, aromatic epoxy resins, epoxidized olefins, brominated resins,aromatic glycidyl amines, heterocyclic glycidyl imidines and amides,glycidyl ethers, fluorinated epoxy resins, or any combination thereof.The difunctional epoxy resin is preferably selected from diglycidylether of Bisphenol F, diglycidyl ether of Bisphenol A, diglycidyldihydroxy naphthalene, or any combination thereof. Most preferred isdiglycidyl ether of Bisphenol F. Diglycidyl ether of Bisphenol F isavailable commercially from Huntsman Advanced Materials (Salt Lake City,Utah) under the trade names Araldite GY281 and GY285 and from Ciba-Geigy(Tarrytown, N.Y.) under the trade name LY9703.

The hybrid polyamide particles may be used to toughen epoxy resincomponents that include trifunctional and/or tetrafunctional epoxyresins other than those previously described. The multifunctional epoxyresins may be saturated, unsaturated, cycloaliphatic, alicyclic orheterocyclic. Suitable multifunctional epoxy resins, by way of example,include those based upon: phenol and cresol epoxy novolacs, glycidylethers of phenol-aldelyde adducts; glycidyl ethers of dialiphatic diols;diglycidyl ether; diethylene glycol diglycidyl ether; aromatic epoxyresins; dialiphatic triglycidyl ethers, aliphatic polyglycidyl ethers;epoxidized olefins; brominated resins; aromatic glycidyl amines;heterocyclic glycidyl imidines and amides; glycidyl ethers; fluorinatedepoxy resins or any combination thereof.

A trifunctional epoxy resin has three epoxy groups substituted eitherdirectly or indirectly in a para or meta orientation on the phenyl ringin the backbone of the compound. A tetrafunctional epoxy resin has fourepoxy groups substituted either directly or indirectly in a meta or paraorientation on the phenyl ring in the backbone of the compound.

The phenyl ring may additionally be substituted with other suitablenon-epoxy substituent groups. Suitable substituent groups, by way ofexample, include hydrogen, hydroxyl, alkyl, alkenyl, alkynyl, alkoxyl,aryl, aryloxyl, aralkyloxyl, aralkyl, halo, nitro, or cyano radicals.Suitable non-epoxy substituent groups may be bonded to the phenyl ringat the para or ortho positions, or bonded at a meta position notoccupied by an epoxy group. Suitable tetrafunctional epoxy resinsinclude N,N,N′,N′-tetraglycidyl-m-xylenediamine (available commerciallyfrom Mitsubishi Gas Chemical Company (Chiyoda-Ku, Tokyo, Japan) underthe name Tetrad-X), and Erisys GA-240 (from CVC Chemicals, Morristown,N.J.)

Suitable trifunctional epoxy resins, by way of example, include thosebased upon: phenol and cresol epoxy novolacs; glycidyl ethers ofphenol-aldelyde adducts; aromatic epoxy resins; dialiphatic triglycidylethers; aliphatic polyglycidyl ethers; epoxidized olefins; brominatedresins, aromatic glycidyl amines and glycidyl ethers; heterocyclicglycidyl imidines and amides; glycidyl ethers; fluorinated epoxy resinsor any combination thereof.

In the DEN/TRIF matrix resin embodiment, the total amount of polyamideparticles in the uncured resin may vary from 9 to 21 weight percentbased on the total weight of the uncured resin. Preferably, the totalamount of polyamide particles in the uncured resin will range from 11 wt% to 19 wt %, based on the total weight of the uncured resin matrix.More preferably, the total amount of polyamide particles in the uncuredresin will range from 12 wt % to 17 wt %, based on the total weight ofthe uncured resin matrix.

In a preferred embodiment, the thermoplastic particle component includesa combination of polyimide particles and hybrid polyamide particles.This particle combination is a preferred thermoplastic particlecomponent for use with the DEN/TRIF/TETF matrix resin embodiment.

Preferred polyimide particles are available commercially from HP PolymerGmbH (Lenzig, Austria) as P84 polyimide molding powder. Suitablepolyamide particles are also available commercially from EvonikIndustries (Austria) under the tradename P84NT. The polyimide used tomake the particles is disclosed in U.S. Pat. No. 3,708,458, the contentsof which is hereby incorporated by reference. The polyimide is made bycombining benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride with amixture of 4,4′-methylenebis(phenyl isocyanate) and toluene diisocyanate(2,4- or 2,6-isomer). The amine analogs may be used in place of thearomatic iso- and diisocyanates. The CAS Registry No. of the polyimideis 58698-66-1.

The polyimide particles are composed of an aromatic polyimide having therepeating monomer formula:

where from 10 to 90% of the R groups in the overall polymer are anaromatic group having the formula:

with the remaining R groups in the polymer being

The size of the polyimide particles in the powder typically ranges from2 microns to 35 microns. A preferred polyimide powder will containparticles that range in size from 2 to 30 microns with the averageparticle size ranging from 5 microns to 15 microns. Preferably, at least90 weight percent of the polyimide particles in the powder will be inthe size range of 2 microns to 20 microns. The polyimide particles maybe regular or irregular in shape. For example, the particles may besubstantially spherical or they can be particles with a jagged shape.

The polyimide particles contain at least 95 weight percent polyimide.Small amounts (up to 5 weight percent) of other materials may beincluded in the particles provided that they do not adversely affect theoverall characteristics of the particles.

The glass transition temperature (Tg) of the polyimide particles shouldbe about 330° C. with the density of individual particles being 1.34grams per cubic centimeter. The linear coefficient of thermal expansionof the particles is 50.

The total amount of thermoplastic particles in the uncured DEN/TRIF/TETFmatrix resin embodiment is preferably from 10 to 20 weight percent basedon the total weight of the uncured resin. In order to obtain highresistance to delamination, the weight ratio between the hybridpolyamide particles and the polyimide particles can range from 3.5:1.0to 1.0:1.0. Preferably, the weight ratio between the hybrid polyamideparticles and polyimide particles is between 3.2:1.0 and 2.8:1.0. In aparticularly preferred DEN/TRIF/TETF matrix resin, the amount of hybridpolyamide particles is from 8 to 10 weight percent of the total weightof the uncured resin and the amount of polyimide particles is from 2 to4 weight percent of the total weight of the uncured resin.

The uncured resin matrix includes at least one curing agent. Suitablecuring agents are those which facilitate the curing of theepoxy-functional compounds of the invention and, particularly,facilitate the ring opening polymerization of such epoxy compounds. In aparticularly preferred embodiment, such curing agents include thosecompounds which polymerize with the epoxy-functional compound orcompounds, in the ring opening polymerization thereof. Two or more suchcuring agents may be used in combination.

Suitable curing agents include anhydrides, particularly polycarboxylicanhydrides, such as nadic anhydride (NA), methylnadic anhydride(MNA—available from Aldrich), phthalic anhydride, tetrahydrophthalicanhydride, hexahydrophthalic anhydride (HHPA—available from Anhydridesand Chemicals Inc., Newark, N.J.), methyltetrahydrophthalic anhydride(MTHPA—available from Anhydrides and Chemicals Inc.),methylhexahydrophthalic anhydride (MHHPA—available from Anhydrides andChemicals Inc.), endomethylenetetrahydrophthalic anhydride,hexachloroendomethylenetetrahydrophthalic anhydride (ChlorenticAnhydride—available from Velsicol Chemical Corporation, Rosemont, Ill.),trimellitic anhydride, pyromellitic dianhydride, maleic anhydride(MA—available from Aldrich), succinic anhydride (SA), nonenylsuccinicanhydride, dodecenylsuccinic anhydride (DDSA—available from Anhydridesand Chemicals Inc.), polysebacic polyanhydride, and polyazelaicpolyanhydride.

Further suitable curing agents are the amines, including aromaticamines, e.g., 1,3-diaminobenzene, 1,4-diaminobenzene,4,4′-diaminodiphenylmethane, and the polyaminosulphones, such as4,4′-diaminodiphenyl sulphone (4,4′-DDS—available from Huntsman),4-aminophenyl sulphone, and 3,3′-diaminodiphenyl sulphone (3,3′-DDS).Also, suitable curing agents may include polyols, such as ethyleneglycol (EG—available from Aldrich), poly(propylene glycol), andpoly(vinyl alcohol); and the phenol-formaldehyde resins, such as thephenol-formaldehyde resin having an average molecular weight of about550-650, the p-t-butylphenol-formaldehyde resin having an averagemolecular weight of about 600-700, and the p-n-octylphenol-formaldehyderesin, having an average molecular weight of about 1200-1400, thesebeing available as HRJ 2210, HRJ-2255, and SP-1068, respectively, fromSchenectady Chemicals, Inc., Schenectady, N.Y.). Further as tophenol-formaldehyde resins, a combination of CTU guanamine, andphenol-formaldehyde resin having a molecular weight of 398, which iscommercially available as CG-125 from Ajinomoto USA Inc. (Teaneck,N.J.), is also suitable.

Different commercially available compositions may be used as curingagents in the present invention. One such composition is AH-154, adicyandiamide type formulation, available from Ajinomoto USA Inc. Otherswhich are suitable include Ancamide 400, which is a mixture ofpolyamide, diethyltriamine, and triethylenetetraamine, Ancamide 506,which is a mixture of amidoamine, imidazoline, andtetraethylenepentaamine, and Ancamide 1284, which is a mixture of4,4′-methylenedianiline and 1,3-benzenedi amine; these formulations areavailable from Pacific Anchor Chemical, Performance Chemical Division,Air Products and Chemicals, Inc., Allentown, Pa.

Additional suitable curing agents include imidazole(1,3-diaza-2,4-cyclopentadiene) available from Sigma Aldrich (St. Louis,Mo.), 2-ethyl-4-methylimidazole available from Sigma Aldrich, and borontrifluoride amine complexes, such as Anchor 1170, available from AirProducts & Chemicals, Inc.

Still additional suitable curing agents include3,9-bis(3-aminopropyl-2,4,8,10-tetroxaspiro[5.5]undecane, which iscommercially available as ATU, from Ajinomoto USA Inc., as well asaliphatic dihydrazide, which is commercially available as Ajicure UDH,also from Ajinomoto USA Inc., and mercapto-terminated polysulphide,which is commercially available as LP540, from Morton International,Inc., Chicago, Ill.

The curing agent(s) is selected so that it provides curing of the matrixat suitable temperatures. The amount of curing agent required to provideadequate curing of the matrix will vary depending upon a number offactors including the type of resin being cured, the desired curingtemperature and curing time. Curing agents typically may also includecyanoguanidine, aromatic and aliphatic amines, acid anhydrides, LewisAcids, substituted ureas, imidazoles and hydrazines. The particularamount of curing agent required for each particular situation may bedetermined by well-established routine experimentation.

Exemplary preferred curing agents include 4,4′-diaminodiphenyl sulphone(4,4′-DDS) and 3,3′-diaminodiphenyl sulphone (3,3′-DDS), bothcommercially available from Huntsman Corporation (The Woodlands, Tex.).

The curing agent is present in an amount that ranges from 10 wt % to 30wt % of the uncured resin matrix. In the DEN/TRIF matrix resin, thecuring agent is present in an amount that ranges from 17 wt % to 27 wt%. More preferably, the curing agent is present in the range 21 wt % to25 wt % of the uncured resin matrix. In the DEN/TRIF matrix resin,4,4′-DDS is a preferred curing agent. It is preferably used as the solecuring agent in an amount ranging from 20 wt % to 26 wt %. Small amounts(less than 5 wt %) of other curatives, such as 3,3′-DDS, may beincluded, if desired.

In the DEN/TRIF/TETF matrix resin, the curing agent is present in anamount that ranges from 15 wt % to 30 wt % of the uncured resin.Preferably, the curing agent is present in an amount that ranges from 20wt % to 30 wt %. 3,3′-DDS is the preferred curing agent. It preferablyused as the sole curing agent in amounts ranging from 24 to 28 weightpercent based on the total weight of the uncured resin. Small amounts(less than 5 wt %) of other curatives, such as 4,4′-DDS, may beincluded, if desired.

Accelerators may also being included to enhance or promote curing.Suitable accelerators are any of the urone compounds that have beencommonly used in the curing of epoxy resins. Specific examples ofaccelerators, which may be used alone or in combination, includeN,N-dimethyl,N′-3,4-dichlorphenyl urea (Diuron), N′-3-chlorophenyl urea(Monuron), and preferably N,N-(4-methyl-m-phenylenebis[N′,N′-dimethylurea] (e.g. Dyhard UR500 available from Degussa).

The uncured resin matrix of the present invention also includes athermoplastic toughening agent. Any suitable thermoplastic polymers maybe used as the toughening agent. Typically, the thermoplastic polymer isadded to the resin mix as particles that are dissolved in the resinmixture by heating prior to addition of the curing agent. Once thethermoplastic agent is substantially dissolved in the hot matrix resinprecursor (i.e. the blend of epoxy resins), the precursor is cooled andthe remaining ingredients (curing agent and insoluble thermoplasticparticles) are added and mixed with the cooled resin blend.

Exemplary thermoplastic toughening agents/particles include any of thefollowing thermoplastics, either alone or in combination: polysulfone,polyethersulfone, polyetherimide, high performance hydrocarbon polymers,elastomers, and segmented elastomers.

A suitable toughening agent, by way of example, is particulatepolyethersulfone (PES) that is sold under the trade name Sumikaexcel5003P, and which is commercially available from Sumitomo Chemicals (NewYork, N.Y.). Alternatives to 5003P are Solvay polyethersulphone 105RP,or the non-hydroxyl terminated grades such as Solvay 1054P which iscommercially available from Solvay Chemicals (Houston, Tex.). DensifiedPES particles may be used as the toughening agent. The form of the PESis not particularly important since the PES is dissolved duringformation of the resin. Densified PES particles can be made inaccordance with the teachings of U.S. Pat. No. 4,945,154, the contentsof which are hereby incorporated by reference. Densified PES particlesare also available commercially from Hexcel Corporation (Dublin, Calif.)under the trade name HRI-1. The average particle size of the tougheningagent should be less than 100 microns to promote and insure completedissolution of the PES in the matrix.

In the DEN/TRIF matrix resin, the toughening agent is present in therange 5 wt % to 15 wt %, based on the total weight of the uncured resinmatrix. Preferably, the toughening agent is present in the range 7 wt %to 12 wt %. More preferably, the toughening agent is present in therange 8 wt % to 11 wt %.

In the DEN/TRIF/TETF matrix resin, the PES toughening agent is presentin the range 5 wt % to 26 wt %, based on the total weight of the uncuredresin. Preferably, the toughening agent is present in the range 7 wt %to 14 wt %. The preferred amount of PES for use in making resins withrelatively low minimum viscosity (25-45 Poise) is from 7 to 9 weightpercent based on the total weight of the uncured resin. The preferredamount of PES for use in making resins with relatively high minimumviscosity (55-75 Poise) is from 10 to 13 weight percent based on thetotal weight of the uncured resin.

The matrix resin may also include additional ingredients, such asperformance enhancing or modifying agents provided they do not adverselyaffect the tack and out-life of the prepreg or the strength and damagetolerance of the cured composite part. The performance enhancing ormodifying agents, for example, may be selected from core shell rubbers,flame retardants, wetting agents, pigments/dyes, UV absorbers,anti-fungal compounds, fillers, conducting particles, and viscositymodifiers.

Exemplary core shell rubber (CSR) particles are composed of acrosslinked rubber core, typically a copolymer of butadiene, and a shellcomposed of styrene, methyl methacrylate, glycidyl methacrylate and/oracrylonitrile. The core shell particles are usually provided asparticles dispersed in an epoxy resin. The size range of the particlesis typically from 50 to 150 nm. Suitable CSR particles are described indetail in U.S. Patent Publication US2007/0027233A1, the contents ofwhich is hereby incorporated by reference. Preferred core shellparticles are MX core-shell particles, which are available from Kane Ace(Pasadena, Tex.). A preferred core shell particle for inclusion in theDEN/TRIF matrix resin is Kane Ace MX-418. MX-418 is supplied as a 25 wt% suspension of core shell particles in a tetrafunctional epoxy resin.The core shell particles in MX-418 are polybutadiene (PBd) core shellparticles which have an average particle size of 100 nanometers.

Suitable fillers include, by way of example, any of the following eitheralone or in combination: silica, alumina, titania, glass, calciumcarbonate and calcium oxide.

Suitable conducting particles, by way of example, include any of thefollowing either alone or in combination: silver, gold, copper,aluminum, nickel, conducting grades of carbon, buckminsterfullerene,carbon nanotubes and carbon nanofibres. Metal-coated fillers may also beused, for example nickel coated carbon particles and silver coatedcopper particles.

Potato shaped graphite (PSG) particles are suitable conductingparticles. The use of PSG particles in carbon fiber/epoxy resincomposites is described in detail in U.S. Patent Publication No. US2015/0179298 A1, the contents of which is hereby incorporated byreference. The PSG particles are commercially available from NGSNaturgraphit (Germany) as SG25/99.95 SC particles or from Nippon PowerGraphite Company (Japan) as GHDR-15-4 particles. These commerciallyavailable PSG particles have average particle sizes of from 10-30microns with the GHDR-15-4 particles having a vapor deposited coating ofcarbon on the outer surface of the PSG particles.

The uncured resin matrix may include small amounts (less than 5 wt % andpreferably less than 1 wt %) of an additional epoxy or non-epoxythermosetting polymeric resin. For DEN/TRIF/TETF matrix resins, theepoxy resin component contains at least 95 wt % DEN, TRIF and TETF andmore preferably at least 99 wt % of the three epoxy resins. For DEN/TRIFmatrix resins, the epoxy resin component contains at least 95 wt % DENand TRIF and more preferably at least 99 wt % of the two epoxy resins.Suitable additional epoxy resins include difunctional epoxy resins, suchas bisphenol A and bisphenol F type epoxy resins. Suitable non-epoxythermoset resin materials for the present invention include, but are notlimited to, resins of phenol formaldehyde, urea-formaldehyde,1,3,5-triazine-2,4,6-triamine (Melamine), bismaleimide, vinyl esterresins, benzoxazine resins, phenolic resins, polyesters, cyanate esterresins or any combination thereof. The additional thermoset resin, ifany, is preferably selected from epoxy resins, cyanate ester resins,benzoxazine and phenolic resins.

The uncured resin is made in accordance with standard prepreg matrixresin processing. In general, the hydrocarbon novolac epoxy resin andother epoxy resin(s) are mixed together at room temperature to form aresin mix to which the thermoplastic toughening agent is added. Thismixture is then heated to about 120° C. for about 1 to 2 hours todissolve the thermoplastic toughening agent. The mixture is then cooleddown to about 80° C. and the remainder of the ingredients (thermoplasticparticle component, curing agent and other additive, if any) is mixedinto the resin to form the final uncured resin matrix that isimpregnated into the fiber reinforcement.

The uncured resin is applied to the fibrous reinforcement to form anuncured resin matrix in accordance with any of the known prepregmanufacturing techniques. The fibrous reinforcement may be fully orpartially impregnated with the uncured resin. In an alternateembodiment, the uncured resin may be applied to the fiber fibrousreinforcement as a separate layer, which is proximal to, and in contactwith, the fibrous reinforcement, but does not substantially impregnatethe fibrous reinforcement. The prepreg, which is also referred to assemi-preg, is typically covered on both sides with a protective film androlled up for storage and shipment at temperatures that are typicallykept well below room temperature to avoid premature curing. The actualresin matrix is not formed until further processing of the semi-preg.Any of the other prepreg manufacturing processes and storage/shippingsystems may be used if desired.

The fibrous reinforcement of the prepreg may be selected from anyfiberglass, carbon or aramid (aromatic polyamide) fibers. The fibrousreinforcement is preferably carbon fibers. Preferred carbon fibers arein the form of tows that contain from 3,000 to 50,000 carbon filaments(3K to 50K). Commercially available carbon fiber tows that contain 6,000or 24,000 carbon filaments (6K or 24K) are preferred.

The uncured matrix resins of the present invention are particularlyeffective in providing laminates that have high strength properties anddamage tolerance when the carbon tow contains from 6,000 to 24,000filaments, the tensile strength is from 750 to 860 ksi, the tensilemodulus is from 35 to 45 Msi, the strain at failure is 1.5 to 2.5%, thedensity is 1.6 to 2.0 g/cm³ and the weight per length is from 0.2 to 0.6g/m. 6K and 12K IM7 carbon tows (available from Hexcel Corporation) arepreferred. IM7 12K fibers have a tensile strength of 820 ksi, thetensile modulus is 40 Msi, the strain at failure is 1.9%, the density is1.78 g/cm³ and the weight per length is 0.45 g/m. IM7 6K fibers have atensile strength of 800 ksi, the tensile modulus is 40 Msi, the strainat failure is 1.9%, the density is 1.78 g/cm³ and the weight per lengthis 0.22 g/m. IM7 fibers and carbon fibers with similar properties aregenerally considered to be intermediate modulus carbon fibers. IM8carbon fibers, which are commercially available from Hexcel Corporation(Dublin, Calif.), are also a preferred type of medium modulus carbonfiber.

The fibrous reinforcement may comprise cracked (i.e. stretch-broken) orselectively discontinuous fibers, or continuous fibers. The use ofcracked or selectively discontinuous fibers may facilitate lay-up of thecomposite material prior to being fully cured, and improve itscapability of being shaped. The fibrous reinforcement may be in a woven,non-crimped, non-woven, unidirectional, or multi-axial textile structureform, such as quasi-isotropic chopped prepreg that is used to form sheetmolding compound. The woven form may be selected from a plain, satin, ortwill weave style. The non-crimped and multi-axial forms may have anumber of plies and fiber orientations. Such styles and forms are wellknown in the composite reinforcement field, and are commerciallyavailable from a number of companies, including Hexcel Reinforcements(Les Avenieres, France).

The prepreg may be in the form of continuous tapes, towpregs, webs, orchopped lengths (chopping and slitting operations may be carried out atany point after impregnation). The prepreg may be an adhesive orsurfacing film and may additionally have embedded carriers in variousforms both woven, knitted, and non-woven. The prepreg may be fully oronly partially impregnated, for example, to facilitate air removalduring curing.

The following exemplary DEN/TRIF/TETF resin formulation may beimpregnated into a fibrous support to form a resin matrix in accordancewith the present invention (all weight percentages are based on thetotal resin weight): 12 wt % to 16 wt % dicyclopentadiene novolac epoxyresin (TACTIX®556 or XD-1000-2L); 17 wt % to 21 wt %triglycidyl-p-aminophenol (MY0510); 16 wt % to 20 wt % tetrafunctionalepoxy (MY721); 10 wt % to 14 wt % polyethersulfone (5003P); 2 wt % to 4wt % polyimide particles (P84HCM); 7 wt % to 11 wt % hybrid polyamideparticles; and 24 wt % to 28 wt % 3,3′-DDS as the curing agent.

With respect to the DEN/TRIF matrix resin embodiments of the invention,an exemplary DEN/TRIF matrix resin includes from 34 wt % to 38 wt %triglycidyl-m-aminophenol (MY0600); from 16 wt % to 20 wt % hydrocarbonnovolac epoxy resin (TACTIX 556 or XD-1000-2L); from 7 wt % to 11 wt %polyethersulfone (5003P) as a toughening agent; from 2 wt % to 7 wt %crosslinked polyamide 12 particles (ORGASOL 2009); from 9 wt % to 13 wt% hybrid polyamide particles where the weight ratio of hybrid polyamideparticles to crosslinked polyamide 12 particles is from 2.5:1.0 to 3.0:1and preferably 2.7:1 to 2.8:1; and from 20 wt % to 26 wt % 4,4′-DDS asthe curing agent.

Another exemplary DEN/TRIF matrix resin includes from 34 wt % to 38 wt %triglycidyl-m-aminophenol (MY0600); from 16 wt % to 20 wt % hydrocarbonnovolac epoxy resin (TACTIX 556 or XD-1000-2L); from 7 wt % to 11 wt %polyethersulfone (5003P) as a toughening agent; from 9 wt % to 13 wt %polyamide 11 particles (Rislan PA11); from 2 wt % to 4 wt % hybridpolyamide particles; and from 20 wt % to 26 wt % 4,4′-DDS as the curingagent.

A preferred DEN/TRIF matrix resin includes from 34 wt % to 38 wt %triglycidyl-m-aminophenol (MY0600); from 16 wt % to 20 wt % hydrocarbonnovolac epoxy resin (TACTIX 556 or XD-1000-2L); from 7 wt % to 11 wt %polyethersulfone (5003P) as a toughening agent; from 13 wt % to 17 wt %hybrid polyamide particles; and from 20 wt % to 26 wt % 4,4′-DDS as thecuring agent.

The prepreg may be molded using any of the standard techniques used toform composite parts. Typically, one or more layers of prepreg areplaced in a suitable mold and cured to form the final composite part.The prepreg of the invention may be fully or partially cured using anysuitable temperature, pressure, and time conditions known in the art.Typically, the prepreg will be cured in an autoclave at temperatures ofbetween 160° C. and 190° C. The composite material may be cured using amethod selected from microwave radiation, electron beam, gammaradiation, or other suitable thermal or non-thermal radiation.

Composite parts made from the improved prepreg of the present inventionwill find application in making articles such as numerous primary andsecondary aerospace structures (wings, fuselages, bulkheads and thelike), but will also be useful in many other high performance compositeapplications including automotive, rail and marine applications wherehigh compressive strength, interlaminar fracture toughness andresistance to impact damage are needed.

Examples 1-2, which are examples of practice with respect to theDEN/TRIF/TETF matrix resin embodiment of the invention, are as follows:

Example 1

A preferred exemplary resin formulation in accordance with the presentinvention is set forth in TABLE 1. A matrix resin was prepared by mixingthe epoxy ingredients at room temperature with the polyethersulfone toform a resin blend that was heated to 120° C. for 60 minutes tocompletely dissolve the polyethersulfone. The mixture was cooled to 80°C. and the rest of the ingredients added and mixed in thoroughly.

The hybrid polyamide particles used in the following examples are listedaccording to the weight percentage of amorphous (Trogamid® CX9704)polyamide and semi-crystalline (Trogamid® CX9705) polyamide that arepresent in each particle. As previously mentioned, hybrid polyamideparticles that contain a mixture of 70 wt % CX9704 polyamide and 30 wt %CX9705 polyamide are identified as hybrid particles “(70A/30SC)”, andhybrid polyamide particles that contain a mixture of 30 wt % CX9704polyamide and 70 wt % CX9705 polyamide are identified as hybridpolyamide particles “(30A/70SC)”. The hybrid polyamide particles used inthe examples, as well as the amorphous and semi-crystalline particlesused in the comparative examples, ranged in particle size from 3 micronsto 10 microns with an average particle size of 6 microns.

TABLE 1 Ingredient Amount (Wt %) Hydrocarbon epoxy novolac resin 14.10(TACTIX ®556) Trifunctional para-glycidyl amine (MY0510) 19.15N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl 17.85 methane (MY721)Thermoplastic Toughening Agent (polyether 11.50 sulfone - 5003P)Polyimide Particles (P84HCM) 3.0 Hybrid Polyamide Particles (70A/30SC)9.0 Aromatic diamine curing agent (3,3-DDS) 25.40

Exemplary prepreg was prepared by impregnating one or more layers ofunidirectional carbon fibers with the resin formulation of TABLE 1. Theunidirectional carbon fibers (12K IM7 available from Hexcel Corporation)were used to make a prepreg in which the matrix resin amounted to 35weight percent of the total uncured prepreg weight and the fiber arealweight was 192 grams per square meter (gsm). 26-ply laminates wereprepared using standard prepreg fabrication procedures. The laminateswere cured in an autoclave at 177° C. for about 2 hours. The curedlaminates were tested to determine interlaminar fracture toughness.

G2c is a standard test that provides a measure of the interlaminarfracture toughness of a cured laminate. G2c was determined as follows. A26-ply unidirectional laminate was cured with a 3 inch fluoroethylenepolymer (FEP) film inserted along one edge, at the mid-plane of thelayup, perpendicular to the fiber direction to act as a crack starter.The laminate was cured for 2 hours at 177° C. in an autoclave and gave anominal thickness of 3.8 mm. Consolidation was verified by C-scan. G2csamples were machined from the cured laminate. G2c was tested at roomtemperature in accordance with BSS7320. The G2c values listed below arethe average of the first and second cracks observed during the testingin accordance with BSS7320.

Cured test laminates were also subjected to standard tests to determinetheir tolerance to damage (CAI) and interlaminar fracture toughness (G1cand G2c). Compression after Impact (CAI) was determined using a 270in-lb impact against a 32-ply quasi-isotropic laminate. The specimenswere machined, impacted and tested in accordance with Boeing test methodBSS7260 per BMS 8-276. Values are normalized to a nominal cured laminatethickness of 0.18 inches.

When the terms “CAI” and “G2c” are used herein to define a propertyexhibited by a cured laminate, the terms mean the property as measuredby the above described testing procedures.

The G2c of the cured 26-ply laminate was 12.6. The CAI was 46.0. Openhole compression (OHT) and open hole compression (OHC) were alsomeasured according to standard procedures at room temperature and foundto be above acceptable limits for structural parts.

Example 2

An exemplary prepreg having a DEN/TRIF/TETR resin matrix with theformula set forth in TABLE 2 was prepared in the same manner as Example1.

TABLE 2 Ingredient Amount (Wt %) Hydrocarbon epoxy novolac resin 14.10(TACTIX ®556) Trifunctional para-glycidyl amine (MY0510) 19.15N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenyl 17.85 methane (MY721)Thermoplastic Toughening Agent (polyether 11.50 sulfone - 5003P)Polyimide Particles (P84HCM) 3.0 Hybrid Polyamide Particle (30A/70SC)9.0 Aromatic diamine curing agent (3,3-DDS) 25.40

26-ply laminates were prepared, cured and tested for G2c at roomtemperature in the same manner as Example 1. The G2c was 11.8 and CAIwas 43.6. The OHT and OHC were both also above acceptable limits forstructural parts. The values for G2c and CAI in Example 2 (hybridparticles 30A/70SC) are unexpectedly less than in Example 1 (hybridparticles 70A/30SC), where the amount of amorphous polyamide in theparticle is substantially greater than the amount of semi-crystallinepolyamide. Accordingly, as previously mentioned, it is preferred thathybrid polyamide particles contain from 60 wt % to 80 wt % amorphouspolyamide and from 20 wt % to 40 wt % semi-crystalline polyamide.

A first comparative example was performed in which semi-crystallinepolyamide particles made from Trogamid® CX9705 polyamide weresubstituted in place of the hybrid polyamide particles used in Examples1 and 2. 26-ply laminates were prepared, cured and tested for G2c atroom temperature in the same manner as Example 1. The G2c was 9.0. CAIwas 43.0. It was unexpected that the G2c and CAI would be lower whenparticles containing only the semi-crystalline form of the polyamidewere substituted in place of the hybrid particles that contain a mixtureof the semi-crystalline form and amorphous form of the same polyamide.

A second comparative example was performed in which amorphous polyamideparticles made from Trogamid® CX9704 polyamide were substituted in placeof the hybrid polyamide particles used in Examples 1 and 2. 26-plylaminates were prepared, cured and tested for G2c at room temperature inthe same manner as Example 1. The G2c was 10.0 and CAI was 44.9. It wasunexpected that the G2c and CAI would be lower when particles containingonly the amorphous form was substituted in place of the hybrid particlesthat contain a 70A/30SC mixture of the amorphous and semi-crystallineforms of the same polyamide, as set forth in Example 1. It was alsounexpected that the G2c of the second comparative example would be lowerwhen particles containing only the amorphous form was substituted inplace of the hybrid particles that contain a 30A/70SC mixture of theamorphous and semi-crystalline forms of the same polyamide, as set forthin Example 2, and that the CAI of the second comparative example washigher than Example 2.

The above examples and comparative examples all use polyamide particlesthat are made from a polyamide that has the same monomeric unit (formulaII). It is unexpected that hybrid polyamide particles, which eachcontain a mixture of amorphous and semi-crystalline forms of the samepolymer, are capable of providing higher G2c and CAI test results thancan be achieved using the amorphous or semi-crystalline form of thepolyamide alone.

Examples 3-5, which are examples of practice with respect to theDEN/TRIF matrix resin embodiment of the invention, are as follows:

Example 3

An exemplary DEN/TRIF resin formulation in accordance with the presentinvention is set forth a TABLE 3. An uncured matrix resin was preparedby mixing the epoxy ingredients at room temperature with thepolyethersulfone to form a resin blend that was heated to 120° C. for 60minutes to completely dissolve the polyethersulfone. The mixture wascooled to 80° C. and the rest of the ingredients were added and mixed inthoroughly in the same manner as Examples 1-2.

TABLE 3 Ingredient Amount (Wt %) dicyclopentadiene novolac epoxy resin(XD- 18.0 1000-2L) Trifunctional meta-glycidyl amine (MY0600) 36.02Thermoplastic Toughening Agent (polyether 9.0 sulfone - 5003P) HybridPolyamide Particles (70A/30SC) 15.0 Aromatic diamine curing agent(4,4′-DDS) 21.98

Exemplary prepreg was prepared by impregnating a layer of unidirectionalcarbon fibers with the resin formulation of TABLE 3 to form a prepregcomposed of reinforcing fibers and an uncured resin matrix. Theunidirectional carbon fibers were 12K IM7. The uncured resin matrixamounted to 35 weight percent of the total uncured prepreg weight andthe fiber areal weight of the uncured prepreg was 145 grams per squaremeter (gsm).

The prepreg was used to form a laminate in the same manner as Examples1-2. The laminate was cured in an autoclave at 177° C. for about 2 hoursto form a cured test laminate. The cured test samples were subjected totesting in accordance with ASTM D5528 in the same manner as Examples 1-2in order to determine G2c and CAI. The G2c was determined to be 18.1 andthe CAI was 55.9.

A comparative example was performed in which semi-crystalline polyamideparticles made from Trogamid® CX9705 polyamide were substituted in placeof the hybrid polyamide particles used in Example 3. 26-ply laminateswere prepared, cured and tested for CAI and G2c at room temperature inthe same manner as Example 1. The CAI was 50.0 G2c was 12.4. It wasunexpected that the G2c would be lower when particles containing onlythe semi-crystalline form of the polyamide were substituted in place ofthe hybrid particles that contain a mixture of the semi-crystalline formand amorphous form of the same polyamide.

A second comparative example was performed in which amorphous polyamideparticles made from Trogamid® CX9704 polyamide were substituted in placeof the hybrid polyamide particles used in Example 3. 26-ply laminateswere prepared, cured and tested for CAI and G2c at room temperature inthe same manner as Example 1. The CAI was 63.2 and G2c was 17.8. It wasunexpected that the G2c would be lower when particles containing onlythe amorphous form was substituted in place of the hybrid particles thatcontain a mixture of the amorphous form and semi-crystalline form of thesame polyamide, as set forth in Example 1. The result is particularlyunexpected in view of the substantially lower G2c that was observed inthe first comparative example.

The above example and comparative examples all use polyamide particlesthat are made from a polyamide that has the same monomeric unit (formulaII). It is unexpected that hybrid polyamide particles, which eachcontain a mixture of amorphous and semi-crystalline forms of the samepolymer, are capable of providing higher G2c test results than can beachieved using the amorphous or semi-crystalline form of the polyamidealone.

Example 4

An exemplary prepreg having a DEN/TRIF resin matrix with the formula setforth in TABLE 4 was prepared in the same manner as Example 3.

TABLE 4 Ingredient Amount (Wt %) dicyclopentadiene novolac epoxy resin(XD- 18.0 1000-2L) Trifunctional meta-glycidyl amine (MY0600) 36.02Thermoplastic Toughening Agent (polyether 9.0 sulfone - 5003P) HybridPolyamide Particles (70A/30SC) 4.0 PA11 Particles (Rislan 11) 11.0Aromatic diamine curing agent (4,4′-DDS) 21.98

26-ply laminates were prepared, cured and tested for CAI and G2c at roomtemperature in the same manner as Example 1. The CAI was 61.6 and G2cwas 16.4. The OHT and OHC were both also above acceptable limits forstructural parts.

Example 5

An exemplary prepreg having a DEN/TRIF resin matrix with the formula setforth in TABLE 5 was prepared in the same manner as Example 3.

TABLE 5 Ingredient Amount (Wt %) dicyclopentadiene novolac epoxy resin(XD- 18.0 1000-2L) Trifunctional meta-glycidyl amine (MY0600) 36.02Thermoplastic Toughening Agent (polyether 9.0 sulfone - 5003P) HybridPolyamide Particles (70A/30SC) 11.0 Crosslinked PA12 Particles (ORGASOL2009) 4.0 Aromatic diamine curing agent (4,4′-DDS) 21.98

26-ply laminates were prepared, cured and tested for CAI and G2c at roomtemperature in the same manner as Example 1. The CAI was 61.2 and G2cwas 16.5. The OHT and OHC were both also above acceptable limits forstructural parts.

Having thus described exemplary embodiments of the present invention, itshould be noted by those skilled in the art that the within disclosuresare exemplary only and that various other alternatives, adaptations andmodifications may be made within the scope of the present invention.Accordingly, the present invention is not limited by the above-describedembodiments, but is only limited by the following claims.

What is claimed is:
 1. A pre-impregnated composite material comprising:A) reinforcing fibers; B) an uncured resin matrix comprising: a) anepoxy resin component comprising a hydrocarbon epoxy novolac resin, atrifunctional epoxy resin and a tetrafunctional epoxy resin; b) athermoplastic particle component comprising a mixture of polyimideparticles and hybrid polyamide particles wherein each of said hybridpolyamide particles comprises a mixture of a semi-crystalline polyamideand an amorphous polyamide, said amorphous polyamide being present in anamount of from 60 to 80 weight percent, based on the total weight ofsaid hybrid polyamide particle, and said semi-crystalline polyamidebeing present in an amount of from 20 to 40 weight percent, based on thetotal weight of said hybrid polyamide particle, and wherein saidsemi-crystalline polyamide and amorphous polyamide are comprised ofdifferent stereo isomeric forms of the polyamide which is the polymericcondensation product of 1,10-decane dicarboxylic acid and an aminecomponent having the formula

c) a thermoplastic toughening agent comprising polyethersulfone; and d)a curing agent.
 2. The pre-impregnated composite material according toclaim 1 wherein said amorphous polyamide is present in an amount of from65 to 75 weight percent, based on the total weight of said hybridpolyamide particle, and said semi-crystalline polyamide being present inan amount of from 25 to 35 weight percent, based on the total weight ofsaid hybrid polyamide particle.
 3. The pre-impregnated compositematerial according to claim 2 wherein said amorphous polyamide beingpresent in an amount of 70±1 weight percent, based on the total weightof said hybrid polyamide particle, and said semi-crystalline polyamidebeing present in an amount of 30±1 weight percent, based on the totalweight of said hybrid polyamide particle.
 4. The pre-impregnatedcomposite material according to claim 1 wherein said reinforcing fiberscomprise a plurality of carbon fiber tows which each comprises from10,000 to 14,000 carbon filaments wherein the weight per length of eachof said carbon tows is from 0.2 to 0.6 grams per meter and wherein thetensile strength of each of said carbon tows is from 750 to 860kilopounds per square inch and the tensile modulus of each of saidcarbon tows is from 35 to 45 megapounds per square inch.
 5. Thepre-impregnated composite material according to claim 1 wherein saidcuring agent is an aromatic amine selected from the group consisting of3,3′-diaminodiphenyl sulphone and 4,4′-diaminodiphenyl sulphone.
 6. Acomposite part or structure that has been formed by curing apre-impregnated composite material according to claim
 1. 7. Thecomposite part or structure according to claim 6 wherein said compositepart or structure forms at least part of an aircraft primary structure.8. A method for making a composite part or structure comprising the stepof providing a pre-impregnated composite material according to claim 1and curing said pre-impregnated composite material to form saidcomposite part or structure.
 9. The method for making a composite partor structure according to claim 8 wherein said composite part orstructure forms at least part of an aircraft primary structure.
 10. Amethod for making a pre-impregnated composite material that is curableto form a composite part, said method comprising the steps of: A)providing reinforcing fibers comprising carbon fibers; and B)impregnating said reinforcing fibers with an uncured resin matrixwherein said uncured resin matrix comprises: a) an epoxy resin componentcomprising a hydrocarbon epoxy novolac resin, a trifunctional epoxyresin and a tetrafunctional epoxy resin; b) a thermoplastic particlecomponent comprising a mixture of polyimide particles and hybridpolyamide particles wherein each of said hybrid polyamide particlescomprises a mixture of a semi-crystalline polyamide and an amorphouspolyamide, said amorphous polyamide being present in an amount of from60 to 80 weight percent, based on the total weight of said hybridpolyamide particle, and said semi-crystalline polyamide being present inan amount of from from 20 to 40 weight percent, based on the totalweight of said hybrid polyamide particle, and wherein saidsemi-crystalline polyamide and amorphous polyamide are comprised ofdifferent stereo isomeric forms of the polyamide which is the polymericcondensation product of 1,10-decane dicarboxylic acid and an aminecomponent having the formula

c) a thermoplastic toughening agent comprising polyethersulfone; and d)a curing agent.
 11. The method for making a pre-impregnated compositematerial according to claim 10 wherein said amorphous polyamide ispresent in an amount of from 65 to 75 weight percent, based on the totalweight of said hybrid polyamide particle, and said semi-crystallinepolyamide being present in an amount of from 25 to 35 weight percent,based on the total weight of said hybrid polyamide particle.
 12. Themethod for making a pre-impregnated composite material that is curableto form a composite part according to claim 10 wherein said amorphouspolyamide being present in an amount of 70±1 weight percent, based onthe total weight of said hybrid polyamide particle, and saidsemi-crystalline polyamide being present in an amount of 30±1 weightpercent, based on the total weight of said hybrid polyamide particle.13. The method for making a pre-impregnated composite material that iscurable to form a composite part according to claim 10 wherein saidreinforcing fibers comprise a plurality of carbon fiber tows which eachcomprises from 10,000 to 14,000 carbon filaments wherein the weight perlength of each of said carbon tows is from 0.2 to 0.6 grams per meterand wherein the tensile strength of each of said carbon tows is from 750to 860 kilopounds per square inch and the tensile modulus of each ofsaid carbon tows is from 35 to 45 megapounds per square inch.
 14. Themethod for making a pre-impregnated composite material that is curableto form a composite part according to claim 10 wherein said curing agentis an aromatic amine selected from the group consisting of3,3′-diaminodiphenyl sulphone and 4,4′-diaminodiphenyl sulphone.